On the date of the bombing, Nichols was hundreds of miles away at his home in Herington, Kansas. Two days later he voluntarily went in for questioning at the Herington Police headquarters, claiming he had heard on the news that he was a material witness. (Terry’s brother James was also held as a material witness, but all charges against him were later dropped.) Two hours into the questioning, a warrant was issued for the arrest of Terry Nichols, although he was questioned for seven more hours before being arrested in connection with the bombing.

The remains of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, destroyed by a terrorist truck bomb on April 19, 1995.David Glass/AP

On May 10, 1995, Nichols was formally charged with the bombing, and three months later, both Nichols and McVeigh were indicted by a federal grand jury. The indictments were identical, charging each man with conspiracy to use a weapon of mass destruction, the use of a weapon of mass destruction, destruction by explosives, and eight counts of first-degree murder for the deaths of federal employees in the Murrah Building.

Timothy McVeigh being escorted from the Noble County Courthouse in Perry, Okla., after being charged for his involvement in the Oklahoma City bombing.David Longstreath/AP Images.

Nichols went on trial three months after McVeigh had been convicted and condemned to death. The prosecution used much of the same evidence and called many of the same witnesses, but the case lacked some of the key elements that had contributed to McVeigh’s conviction, such as a strong antigovernment motive and significant physical evidence. The government alleged that Nichols, using the alias “Mike Havens,” purchased 40 50-pound bags of ammonium nitrate fertilizer—the main ingredient in the Oklahoma City bomb—from a farm co-op in McPherson, Kansas, on September 30, 1994.

From that date forward, the prosecution linked Nichols to several key stages in the plot, including renting storage lockers and stealing 299 sticks of water-gel explosives, 544 blasting caps, and detonating cord from a quarry in Marion, Kansas, on October 1, 1994. Fingerprint evidence found on a receipt in Nichols’s wallet confirmed that Nichols and McVeigh were together on April 13, 1995. Other circumstantial evidence connected Nichols to the robbery of a gun collector in Arkansas, which the prosecution claimed was to fund the bombing conspiracy. The prosecution also suggested that Nichols drove McVeigh from Junction City, Oklahoma, to Oklahoma City on April 16, 1995, to drop off the getaway car. Nichols’s wife, Marife Nichols, could not testify to his whereabouts on April 18; his former wife, Lana Padilla, testified that Nichols had left a package with her to be opened in the event of his death while he was away in the Philippines. In this package, she found a letter written to McVeigh in which Nichols urged McVeigh to “Go for it!”

Late in 1997 the federal jury found Nichols guilty on one count of conspiracy and eight counts of involuntary manslaughter. Nichols was spared the death sentence because of a deadlocked jury. In mid-1998 he was sentenced to life in prison without possibility of parole.

Over the next several years, Nichols lost a series of appeals, including efforts to block a trial for state charges, which included 161 counts of first-degree murder for which Nichols could have still received the death penalty. The state trial took place in 2004, and although the jury convicted Nichols on all murder charges, as well as conspiracy and arson charges, the jury members disagreed on whether or not to give him the death penalty. Because Oklahoma requires the unanimous agreement of a jury to enact the death penalty, it was not an option. In 2004 Nichols received a further sentence of 161 consecutive life sentences without possibility of parole.